Near-infrared counterparts of Chandra X-ray sources toward the Galactic Center

Abstract

The Chandra X-ray Observatory has now discovered nearly 10,000 X-ray point sources in the 2 x 0.8 degree region around the Galactic Center (Muno 2009). The sources are likely to be a population of accreting binaries in the Galactic Center, but little else is known of their nature. We obtained JHKs imaging of the 17'x 17' region around Sgr A*, an area containing 4339 of these X-ray sources, with the ISPI camera on the CTIO 4-m telescope. We cross-correlate the Chandra and ISPI catalogs to find potential IR counterparts to the X-ray sources. The extreme IR source crowding in the field means that it is not possible to establish the authenticity of the matches with astrometry and photometry alone. We find 2137 IR/X-ray astrometrically matched sources: statistically we estimate that our catalog contains 289 +/- 13 true matches to soft X-ray sources and 154 +/- 39 matches to hard X-ray sources. However, the fraction of true counterparts to candidate counterparts for hard sources is just 11 %, compared to 60 % for soft sources, making hard source NIR matches particularly challenging for spectroscopic follow-up. We calculate a color-magnitude diagram (CMD) for the matches to hard X-ray sources, and find regions where significant numbers of the IR matches are real. We use their CMD positions to place limits on the absolute Ks band magnitudes of the potential NIR counterparts to hard X-ray sources. We find regions of the counterpart CMD with 9 +/- 3 likely Wolf-Rayet/supergiant binaries (with 4 spectroscopically confirmed in the literature) as well as 44 +/- 13 candidates that could consist of either main sequence high mass X-ray binaries or red giants with an accreting compact companion. (abridged)

39 pages, 9 figures, accepted by Astrophysical Journal

References in corpus (12)

• The UKIRT Infrared Deep Sky Survey (UKIDSS)
• The UKIDSS Galactic Plane Survey
• The UKIRT Wide Field Camera ZYJHK Photometric System: Calibration from 2MASS
• The Donor Stars of Cataclysmic Variables
• A Catalog of X-ray Point Sources from Two Megaseconds of Chandra Observations of the Galactic Center
• Interstellar Extinction Law toward the Galactic Center II: V, J, H, and Ks Bands
• A Chandra Catalog of X-ray Sources in the Central 150 pc of the Galaxy
• The complex, variable near infrared extinction towards the Nuclear Bulge
• The Nature of the Hard-X-Ray Emitting Symbiotic Star RT Cru
• Near-Infrared Counterparts to Chandra X-ray Sources toward the Galactic Center. I. Statistics and a Catalog of Candidates
• Identification of the Infrared Counterpart to a Newly Discovered X-ray Source in the Galactic Center
• The FLAMINGOS-2 Galactic Center Survey

Cited by in corpus (5)

• The Swift Bulge Survey: optical and near-IR follow-up featuring a likely symbiotic X-ray binary & a focused wind CV
• Variability of Optical Counterparts in the Chandra Galactic Bulge Survey
• Near-infrared counterparts to the Galactic Bulge Survey X-ray source population
• Three New Galactic Center X-ray Sources Identified with Near-Infrared Spectroscopy
• The 2013 outburst of a transient very faint X-ray binary, 23" from Sgr A*